/*-------------------------------------------------------------------------
 *
 * superuser.c
 *      The superuser() function.  Determines if user has superuser privilege.
 *
 * All code should use either of these two functions to find out
 * whether a given user is a superuser, rather than examining
 * pg_authid.rolsuper directly, so that the escape hatch built in for
 * the single-user case works.
 *
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      src/backend/utils/misc/superuser.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "catalog/pg_authid.h"
#include "utils/inval.h"
#include "utils/syscache.h"
#include "miscadmin.h"


/*
 * In common cases the same roleid (ie, the session or current ID) will
 * be queried repeatedly.  So we maintain a simple one-entry cache for
 * the status of the last requested roleid.  The cache can be flushed
 * at need by watching for cache update events on pg_authid.
 */
static Oid    last_roleid = InvalidOid;    /* InvalidOid == cache not valid */
static bool last_roleid_is_super = false;
static bool roleid_callback_registered = false;

static void RoleidCallback(Datum arg, int cacheid, uint32 hashvalue);


/*
 * The Postgres user running this command has Postgres superuser privileges
 */
bool
superuser(void)
{
    return superuser_arg(GetUserId());
}


/*
 * The specified role has Postgres superuser privileges
 */
bool
superuser_arg(Oid roleid)
{
    bool        result;
    HeapTuple    rtup;

    /* Quick out for cache hit */
    if (OidIsValid(last_roleid) && last_roleid == roleid)
        return last_roleid_is_super;

    /* Special escape path in case you deleted all your users. */
    if (!IsUnderPostmaster && roleid == BOOTSTRAP_SUPERUSERID)
        return true;

    /* OK, look up the information in pg_authid */
    rtup = SearchSysCache1(AUTHOID, ObjectIdGetDatum(roleid));
    if (HeapTupleIsValid(rtup))
    {
        result = ((Form_pg_authid) GETSTRUCT(rtup))->rolsuper;
        ReleaseSysCache(rtup);
    }
    else
    {
        /* Report "not superuser" for invalid roleids */
        result = false;
    }

    /* If first time through, set up callback for cache flushes */
    if (!roleid_callback_registered)
    {
        CacheRegisterSyscacheCallback(AUTHOID,
                                      RoleidCallback,
                                      (Datum) 0);
        roleid_callback_registered = true;
    }

    /* Cache the result for next time */
    last_roleid = roleid;
    last_roleid_is_super = result;

    return result;
}

/*
 * RoleidCallback
 *        Syscache inval callback function
 */
static void
RoleidCallback(Datum arg, int cacheid, uint32 hashvalue)
{
    /* Invalidate our local cache in case role's superuserness changed */
    last_roleid = InvalidOid;
}
